1. Field of the Invention
The present invention relates to new ionic photoacid generator (PAG) compounds and photoresist composition that include such compounds. In particular, the invention relates to a novel class of ionic PAGs that contain organic onium cations and new sulfonate compounds with no perfluorooctyl sulfonates (no-PFOS) anions. The new PAG anions address the combination of environmental and performance concerns raised by PFOS based PAGs.
2. Description of Related Art
Several acid catalyzed chemically amplified resist compositions have been developed. Chemically amplified resist compositions generally comprise a photosensitive acid (“photoacid”) generator (PAG) and an acid sensitive polymer (resist). Upon exposure to radiation (e.g., x-ray radiation, ultraviolet radiation), the photoacid generator, by producing a proton, creates a photogenerated catalyst (usually a strong acid) during the exposure to radiation. During a post-exposure bake (PEB), the acid may act as a catalyst for further reactions. For example, the acid generated may facilitate the deprotection or cross-linking in the photoresist. The generation of acid from the PAG does not necessarily require heat. However, many known chemically amplified resists require a post-exposure bake (PEB) of one to two minutes in length to complete the reaction between the acid moiety and the acid labile component. The chemical amplification type resist materials include positive working materials that leave the unexposed material with the exposed areas removed and negative working materials that leave the exposed areas with the unexposed areas removed.
On use of the chemical amplification type, positive working, resist compositions, a resist film is formed by dissolving a resin having acid labile groups as a binder and a compound capable of generating an acid upon exposure to radiation (to be referred to as photoacid generator) in a solvent, applying the resist solution onto a substrate by a variety of methods, and evaporating off the solvent optionally by heating. The resist film is then exposed to radiation, for example, deep UV through a mask of a predetermined pattern. This is optionally followed by post-exposure baking (PEB) for promoting acid-catalyzed reaction. The exposed resist film is developed with an aqueous alkaline developer for removing the exposed area of the resist film, obtaining a positive pattern profile. The substrate is then etched by any desired technique. Finally the remaining resist film is removed by dissolution in a remover solution or ashing, leaving the substrate having the desired pattern profile.
The chemical amplification type, positive working, resist compositions adapted for KrF excimer lasers generally use a phenolic resin, for example, polyhydroxystyrene in which some or all of the hydrogen atoms of phenolic hydroxyl groups are protected with acid labile protective groups. Onium salts, such as iodonium salts and sulfonium salts having perfluorinated anion, are typically used as the photoacid generator. If necessary, there are added additives, for example, a dissolution inhibiting or promoting compound in the form of a carboxylic acid and/or phenol derivative having a molecular weight of up to 3,000 in which some or all of the hydrogen atoms of carboxylic acid and/or phenolic hydroxyl groups are protected with acid labile groups, a carboxylic acid compound for improving dissolution characteristics, a basic compound for improving contrast, and a surfactant for improving coating characteristics.
Ionic photoacid generators, preferably onium salts, are advantageously used as the photoacid generator in chemical amplification type resist compositions, especially chemical amplification type, positive working, resist compositions adapted for KrF excimer lasers because they provide a high sensitivity and resolution and are free from storage instability.
As stated above, photoacid generators (PAGs), play a critical role in a chemical amplified resist systems. Among the various classes of ionic and nonionic PAGs that have been developed, one of the most widely used classes is the perfluorinated onium salts. Recently, government action has made the use of the most effective PAGs based on perfluorooctyl sulfonates (PFOS), no longer viable. In addition to environmental concerns, the PFOS-based PAGs are a concern due to their fluorous self-assembly and their diffusion characteristics at smaller dimension. Previous efforts to develop new PAGs have focused mainly on improvement of the photosensitive onium cation side to increase the quantum yield or to improve the absorbance. The nature of the photoacid produced upon irradiation of the PAG is directly related to the anion of the ionic PAG. Difference in acid strength, boiling point, size, miscibility, and stability of the photoacid produced can affect the parameters related to photoresist performance, such as deprotection (or cross-linking) efficiency, photospeed, post exposure bake (PEB) sensitivity, post-exposure delay (PED) stability, resolution, standing waves, image profiles, and acid volatility. Thus, novel PAG anions that can tackle these environmental and performance issue are needed.